Method for producing concrete and reinforced concrete slabs and substantially flat structural elements



3,250,835 METHOD FOR PRODUCING CONCRETE AND REINFORCED CONCRETE SLABS May 10, 1966 N. .1. KOZLOV AND SUBSTANTIALLY FLAT STRUCTURAL ELEMENTS Filed April 30, 1963 6 Sheets-Sheet 1 May 10, 1966 N. J. KOZLOV 3,250,835

METHOD FOR PRODUCING CONCRETE AND REINFORCED CONCRETE SLABS AND SUBSTANTIALLY FLAT STRUCTURAL ELEMENTS Filed April 30. 1963 6 Sheets-Sheet 2 May 10, 1966 N. .1. KOZLOV 3,250,835

METHOD FOR PRODUCING CONCRETE AND REINFORCED CONCRETE SLABS AND SUBSTANTIALLY FLAT STRUCTURAL ELEMENTS Filed April 30, 1963 6 SheetsSheet 5 '12 FIG]. 26

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METHOD FOR PRODUCI CR AN EINF ED GONG E SLABS AND SUBST IALLY T STRUCTU ELEMEN Filed April 30, 1963 6 Sheets-Sheet 6 United States Patent 3,250,835 METHOD FOR PRODUCING CONCRETE AND RE- INFORCED CONCRETE SLABS AND SUBSTAN- TIALLY FLAT STRUCTURAL ELEMENTS Nickolai Jakovlevich Kozlov, Moscow, U.S.S.R., assignor to Spetsialnoje Konstruktorskoje Bureau Prokatdetal Filed Apr. 30, 1963, Ser. No. 276,725 Claims. (Cl. 264-71) This invention relates to methods for the continuous production of reinforced concrete and particularly flat structural elements.

More specifically, the method comprehends the use of an endless plate conveyor provided with interchangeable molding devices, preferably with the conveyor having a speed pre-set in accordance with the time required for hardening of the concrete for obtaining the specified demolding strength, and also with the length of the conveyor section reserved for this purpose, and wherein the concrete mix being continuously fed onto the plate conveyor and spread over its entire width is continuously and successively subjected to the following operation:

molding and compaction on the vibrating plate of the conveyor;

heat-treatment, mainly with steam, within a heat-insulated chamber which encloses the upper flight of the plate conveyor;

automatic separating when the conveyor travels around the sprocket of the conveyor driving station.

Similar methods for continuous production of concrete structural elements are known from British Patent No. 670,796 which covers a conveyor plant incorporating an endless plate conveyor and interchangeable mold side and bottom elements intended for the production of prestressed reinforced concrete bars of T-section. According to the patent, the following separate units are installed successively along the conveyor:

(1) A distributing slot-type bunker with a movable service hopper resting upon the edges of the lower bunker and provided with a hand-operated sector gate;

(2) A vibratory beam for pressing the working arm of the plate conveyor upward and located under the distributing slot-type bunker;

(3) A heat-insulated chamber enclosing the working flight of the plate conveyor and accommodating perforated steam feed pipes; and

(4) Curvilinear guides for receiving the molded workpieces released from the plate conveyor after automatic demolding.

This installation, similar to other equipment of this type such as U.S Patent No. 2,804,672, does not provide for the continuous production of structural elements with the employment of modern techniques which ensure a noteworthy improvement of the physical and mechanical properties of the concrete, increase the number of typesizes of the articles which can be produced, and assure higher technical and economic properties of the manufact-ured articles together with a reduction in weight and overall dimensions of the equipment.

The present method for the continuous production of concrete structural elements is based on a novel sequence of steps in connection with a continuously moving endless plate conveyor provided with interchangeable mold side and bottom elements and having a speed dependent upon the period for hardening of the concrete, and upon the length of the conveyor section allotted for the hardening of the concrete.

More specifically, the method includes the following:

(a) Molding and compacting the mix placed on the vibrating plate of the conveyor, with simultaneous application of a vibrating load from above;

3,250,835 Patented May 10, was

(c) Smoothing of the surface of the mix contained in the mold by means of a bar oscillating in a horizontal plane;

(d) Calibrating and rolling the workpiece by an endless belt travelling around the driving drums and the rolls;

(e) Secondary smoothing of the workpiece surface;

(f) Heat treatment mainly with live steam within a heat-insulated chamber enclosing the working flight of the plate conveyor, with the surface of concrete being hermetically sealed and subjected to a pressure of not less than g./cm. and

(g) Automatic separating with a subsequent discharge of the finished article in a horizontal direction.

Generally, the present apparatus includes an endless plate conveyor provided with interchangeable mold side and bottom elements, a device for coating the surface of the conveyor and the mold elements with a compound pos sessing anti-adhesive properties, a mix spreader a vibratory beam urged upwardly to the lower surface of the working flight of the plate conveyor, a heat-insulated chamber for enclosing the working flight ,of the plate conveyor and accommodating perforated pipes for feeding the heat-transfer medium, and demolding devices.

More particularly, the apparatus includes:

(1) An additional vibratory load installed over the plate conveyor above the vibratory beam;

(2) A two-start helical cutter for the removal of the surplus mix, and a conveyor for the delivery thereof to the spreader;

3) A concrete surface smoother in the shape of a bar and with a drive for imparting horizontal oscillations thereto;

(4) Calibrating and rolling equipment movable in a vertical plane above the plate conveyor and defined by an endless flat belt travelling around the driving drums and the rolls;

(5) A smoother for the post-calibration smoothing of the mix surface in the shape of a horizontally oscillating bar;

(6) A flat endless belt, the lower flight ofwhich enters level with the top surface of the concrete mix the heatinsulated chamber for the heat treatment of the concrete, with such belt being held to the mix surface by means of rolls and travelling around the drums which are freely mounted on their shafts;

(7) A by-passing two-speed roller bed installed on the side of the plate conveyor driving station, with the roller bed ensuring automatic separation in the horizontal direction of extra-long finished articles, and a manipulator for swinging the finished structural element from the horizontal to the vertical position.

Further objects and advantages of the invention will become more readily apparent from the following detailed description and annexed drawings, in which:

FIG. 1 is a longitudinal vertical sectional view of the apparatus,

FIG. 2 is a top plan view of the apparatus,

FIG. 3 is a vertical cross-section taken HI-III of FIG. 1;

FIG. 4 is a vertical cross-section taken IV-IV of FIG. 1,

FIG. 5 is a vertical cross-section taken VV of FIG. 1,

FIG. 6 is a vertical cross-section taken VI-VI of FIG. 1,

FIG. 7 is a vertical cross-section taken along line VII-VII of FIG. 1,

FIG. 8 is a perspective view of a plane reinforced concrete slab,

along line along line along line along line 3 FIG. 9 is a perspective view of a ribbed reinforced concrete slab with untrimmed edges,

FIG. is a perspective view of a multi-ribbed reinforced concrete slab trimmed on two sides,

FIG. 11 is a perspective view of a multi-ribbed reinforced concrete slab trimmed over the entire perimeter,

FIG. .12 is a view of a multi-ribbed reinforced concrete trimmed panel with apertures (without heat insulation),

FIG. 13 is a perspective view of a two-layer panel with apertures, which consists of two multi-ribbed slabs with a heat-sound insulating layer therebetween and fastened together by clamps, and

FIG. 14 is a perspective view of a two-layer reinforced concreteslab without apertures, which consists of two multi-ribbed slabs fastened together by clamps and a layer of sound insulating material being placed along the perimeter of the slab.

The drawings show the apparatus used for the production of heavy-ribbed slabs (shells) having three-dimensional steel reinforcement of steel rods, the conveyor carrying appropriately spaced mold side and bottom elements including the inserts required for forming cavities in the molded slab.

All the units, parts and separate mechanisms of the apparatus are installed on continuous foundation 1. The closed part of the foundation accommodates pits for the steam traps and sludge collectors, while in the section where heat-treatment takes place, as will be later described, there is a heat-insulated chamber 2 through which passes the upper flight of a conveyor plate type belt 3. At the right-hand end of the foundation 1 is located a tensioning station 4, and at the left-hand end a driving station 5 for the conveyor belt 3. The upper flight of the conveyor belt 3 moves from the right to the left, as indicated by'the arrows in FIG. 2.

Links 6 of the conveyor belt 3 have a width-of 300 mm. and a length of 3660 mm., and are made of rolled trough steel. Each link 6 is provided with three rigidly connected supporting rollers 7 freely rotatable on their shafts and movable along rails 8 (FIG. 4).

Side mold elements 9 can be of a length of rolled steel forms attached to the flat outside surface of the links 6, and such elements arereadily interchangeable. In the particular embodiment under consideration, mold bottom elements 10, namely, the cavity-forming inserts, are in the shape of truncated pyramids having rounded corners and edges, and the pyramids are arranged in rows on the conveyor 3. The height of the pyramids is smaller than the overall thickness of slab 11 by a value equal to the shell dome thickness.

Between the tensioning station 4 and molding section on plate 3 there is a free space for installing the mold side and bottom elements and for placing the reinforcing frames.

To provide for the coating of the surface of the conveyor 3 with a compound heated to 70 C., preferably with petrolatum, for preventing the sticking of the concrete to the mold, sprayers 12 are installed in the zone of the driving station 5, with such sprayers being movable when required.

The means for molding and compacting the moving concrete mix comprises a concrete-discharging hose 13 movable in a horizontal plane, a concrete spreader 14, a vibratory beam 15 below the conveyor and vibratory board 16 above the conveyor (FIG. 2).

The hose 13 is attached to the outlet of a continuousaction concrete mixer 17 mounted on a vertical shaft and provided with a mechanism for swinging the same in a horizontal plane alternatively to the right and left through an angle of Following the above, the hose 13 makes lateral movements across the conveyor thereby uniformly distributing the plastic concrete mix over the surface of the conveyor 3. A plow-type spreader 14 is located below the hose 13 and is secured to the body of the vibratory board 16. The spreader is provided with a blade 18 and a nut 19 freely rotatable on a reversible threaded shaft 20 extending transversely relative to the conveyor.

The beam 15, as mentioned above, is located under the conveyor 3 and is perpendicular to the longitudinal center line of the conveyor in the zone of movement of the spreader 14. The beam 15 is in the form of a welded rigid box-shaped structure bearing at its ends upon four spring shock absorbers 21 attached to a supporting frame 22 mounted on a separate foundation or base (not shown) which is isolated from the main foundation 1 by means of vibrating-deadening liners (not shown). The position of the beam 15 is controlled by means of flexible slings (not shown). Vibrations are generated by the unbalanced weights having one and the same direction of eccentricity and fitted on a shaft 23 which is perpendicular to the longitudinal center line of the conveyor. The beam 15 is held against the links of the conveyor 3 by the shock absorbers 21.

The vibratory board 16 is constituted by a vertically movable component 24 having an adjustable angle of inclination and which is installed across the conveyor and carries a vibrator 25. The component 24 compacts the surface of the mix and smooths the same while simultaneously removing rough places thereby preliminarily ensuring the required thickness for the workpiece. The board 16 provides for better compacting of the concrete and surface smoothing, without lapses or displacement of the layers, and in addition the vibration prevents sticking "of the concrete mix to the component 24 and the scoring of the surfaces.

In advance of the spreader 14 are located longitudinal ski-shaped guides 26 for retaining reinforcing frames and separation partitions 27 in the required position and for preventing the distortion thereof.

Following the board 16 is a cutter 28 operable for removing the surplus concrete mix, with due allowance for concrete compacting in the course of subsequent calibration and rolling. The cutter 28 includes a mechanism ensuring its lifting in a vertical plane, and embodying a rotary drive (not shown). The cutter is in the form of a pipe provided with welded helical blades, and it can be seen the same is mounted above the conveyor 3 and extends across the conveyor. The helical blades of the cutter are constituted by two halves which are oppositely directed and upon rotation, the blades force the removed concrete mix towards the middle and then transfer the same to a scraper conveyor 29'wl1ich delivers surplus concrete under the spreader 14. The conveyor 29 is adjustable in a vertical plane.

Following the cutter 28 is a smoother 30 serving for smoothing the surface of the concrete provided with a crank drive (not shown) for ensuring its transverse horizontal oscillations with relation to the conveyor 3.

A set of rolling and calibrating equipment installed after the smoother 30 is assembled in the form of an overhead cage (not shown) enclosing the conveyor 3 and carries two heavy-weight end drums 31 and a plurality of pressingdown rolls 32 mounted in a common frame 34. The rolls support an endless flat strip 33 of rubberized cloth or steel and is attached to the cage by adjusting screws 35 which transmit vertical controllable force to the slabs 11 being calibrated by the rolling. To assure high accuracy of calibration, the conveyor 3 resets upon a plurality of movable endless chain supports 36 provided with rollers 37 which roll on a bearing calibrating plate 38.

The flat strip 33 which is trained over drums 31 and rolls 32 is provided with a cleaning brush device (not shown) having the shape of a shaft installed parallel to the axis of the drum 31, and the shaft is fitted with longitudinal rubber fins and a trough for collecting concrete particles.

The bottom points of the periphery of the drums 31 and rolls 32 lie in one and the same plane and in the course of calibration and rolling, each roll 32 presses upon the surface of the concrete through the strip 33, so that the pressure is applied to a narrow section of the slab with the specific force thus reaching ahigh value.

One of t-he'drums 31 isdriven from the shaft of the tensioning station 4 by virtue of which the speeds of movement of strip 33 and conveyor 3- are always adequately coordinated, thus preventing any likelihood of'displacement in the concrete bulk. By means of the adjusting screws 35 the entire assemblage of drums-31 and rolls 32 can be shifted froma strictly horizontal position to an inclined position.

The final finishing of the surface of the concrete is effected by means of a smoother 39 which structurally is similar to that of the smoother 30.

After the set of calibration and rolling equipment and thesmoother 39 is located a driveless endless fiat rubber belt 40 trained about drums 41 and rolls 42. The latter press down the lower flight of belt 40 to thesurface of the setting concrete for ensuring a pressure of not less than 150 g./cm. The belt 40 which moves freely together with the concrete, covers the concrete within the limits of chamber 2, namely, throughout the entire length of the accelerated hardening section, thereby isolating the concrete from the direct effect of the heat-transfer me- .dium.

The rolls 42 are located in the front part of chamber 2,

as viewed in the direction of movement of belt 40, and are installed on a frame or support 43. The shafts of the rolls 42 move freely in vertical slots and the support 43 is mounted on jack screws 45. The rear drum 41 is provided with a brush cleaner (not-shown) intended for removing particles of concrete.

To assure a more reliable protection for the concrete against the direct influence of the heat-transfer medium, the top pressing arrangement is provided on its sides with vertical screens 44 of a material which remains heat-proof at 110 C., and other openings and gaps are protected by similar screens. As a result, heating of the concrete by the heat-transfer medium is effected only due to the heat transfer through conveyor 3, belt 40 and sides 9.

,At the locations where the conveyor 3 enters or leaves the chamber 2 are exhaust blowers (not shown). On leaving the heat-treatment chamber and reaching the end section of the apparatus, the concrete slabs 11 which have acquired the specified hardness are automatically separated from the conveyor 3, following the movement of the plates 6 over the sprockets of the driving station 5, after which the slabs continue to move in a horizontal plane. The free and automatic separation of the slabs 11, including their separation from the inserts 10, without any distortion or edge breaking, is ensured'due the articulated and coaxial connection of the rear ends of the plates 6 with the links of the hauling chains (not shown), with the pitch of said chains being divisible by the width of the plates 6 of the conveyor 3.

After separation from the conveyor 3 and moving along a horizontal line, the finished slabs 1-1 reach supports 46 and therefrom a motor-driven chain by-pass conveyor 47 rated for two alternative speeds. The first speed is equal to that of the conveyor 3, while the second speed is much higher. From the conveyor 47, the slabs 11 are transferred at a high speed onto a manipulator 48. The manipulator swings the finished slab 11 through an angle of 8085, after which the slab is removed by means of a hoist and transported in a vertical position to the plant storehouse for temporary storage.

The entire complex of the process according to the invention is effected on the conveyor which constantly moves at a uniform speed selected in conformity with the type of workpiece in consideration (mainly, with the slab thickness). In each particular case the speed shall be determined from the formula:-

.6 where:

V=the speed of movement of the conveyor belt (m./min.),

L=the length of'heat-treatment chamber, and

t=the time of solidified concrete curing in the heat-treatment chamber (min).

The mold side and bottom elements are gradually replaced in the free section of. the conveyor 3. The compound for preventing sticking of the concrete to metal (petrolatum) is applied to the outside surfaces of the conveyor-and mold elements by continuous spraying. After such operation, the=reinforcing framework and inserts are placed'on-the conveyor with the aid of a telpher.

The plastic concrete mix prepared in the mixer 17 is continuously fed onto the conveyor 3 and is spread thereon in such a way that the elevation of the surface of the concrete is 3% to 5% higher than that of the project elevation.

The spreading of the concrete mix is accompanied by its molding and preliminary compacting by vibration, using the additional vibratory board and as a result of the preliminary compacting, the elevation of the surface of the concrete is 2% to 4% higher than that of the project elevation.

Next, the roughness of theconcrete surface is eliminated so that the elevation of the surface is 1% or 2% higher than the project elevation, and after which operation the surface is smoothed by transverse horizontally-directed oscillations. The removed surplus of concrete is delivered or returned to the place of its'spreading.

After the surface of concrete is levelled and is strictly horizontal, and is adequately smoothed, its elevation is 1% or 2% higher than that of the project elevation, the workpiece is subjected to calibration and rolling during which the final compaction of the concrete to a ratio of 0.93-0.97, and the precision calibration of the workpiece is effected. At this stage, the rolls apply high pressure to the workpiece, and the elevation of the upper surface of the workpiece is brought down to the project value.

The workpiece is then subjected to a second smoothing by transverse horizontally-directed oscillations, thus obtaining the required finish to the surface of the slab. Thereafter, the workpiece undergoes an accelerated heattreatment, with the surface of the concrete being covered, and a load of not less than 150 g./cm. being applied. At this stage, during the first 30 to 40 min., the concrete workpiece is subjected to an encompassing heating by the heat-transfer medium applied through the cover, such as by steam having a temperature of 105 to 110 C. During the subsequent to min., the heating is discontinued and the temperature of the concrete is maintained within to 98 C.

After leaving the heat-treatment chamber 2, the workpiece which has solidified and acquired the necessary strength is automatically separated and this is achieved due to thefact that the plates of the conveyor 3 move from under the workpiece over the drum of the driving station 5. The slab is thus released and is now ready for transfer to the storehouse for the finished articles.

The process for the continuous production of reinforced concrete slabs in the apparatus described above, in accordance with the invention, is embodied under the following conditions and in the following sequence, conformable to the production of heavy-ribbed shell-type slabs.

For producing reinforced concrete slabs conventional grades of concrete mix should be used, with the mix possessing the required properties as regards strength and other characteristics. In all cases of slab manufacture, stiff concrete mix should be used. The mix should be prepared with the use of a clinker quick-hardening cement having a specific surface of not less than 3500-4000 cm. g. The cement clinker should contain, for example, 55% to 60% of tricalcium silicate and 11% of tricalcium aluminate. In the production of'slabs the use of cement grades with variable mineralogical composition, or mixing of two different cement grades, shall not be allowed.

Maximum efficiency of the production process is ensured when the concrete mix has a temperature during the molding stage of 20 C. and above.

The successive order of working operations is as follows:

The side elements 9, elements 10, transverse separating partitions 27 and the inserts necessary for manufacturing panels with window or'door openings, etc. (not shown), should be installed on the conveyor -3. All the :surfaces which will come in contact with the concrete should be coated with a thin film of an anti-adhesion compound which is applied by the sprayer 1'2, and an example of an effective anti-adhesive compound is pure petrolatum heated to 70 or 80 C.

After the conveyor 3 is coated with such compound, prefabricated three-dimensional reinforcing frames and inserts (not shown) should be placed on the conveyor with the aid of a hoist, or manually. When the belt 3 carrying the reinforcing frames is in movement, the concrete mix is continuously fed onto the conveyor through the hose 13, with the mix being supplied from the concrete-preparation plane which is either an integral part of the plant or an independent installation.

The concrete mix is uniformly distributed on the surface of the conveyor 3 by the spreader 14, and is compacted due to the combined effect of the vibratory beam 15 and vibratory board 16.

When the workpiece passes under the cutter 28, a layer of concrete is removed with due allowance for subsequent compacting in the range of 3% to 5% of the specified workpiece thickness, and the removed surplus is reclaimed by means of the conveyor 29and returned under the spreader 14.

Next, the workpiece is subjected to treatment by the rolling and calibration equipment and, due to the action of the rolls 32, is finally compacted and calibrated to the specified thickness, with the simultaneous smoothing of its surface. During calibration, the force applied to the slab by the rolls 32 and drums 31 is varied by lifting such rolls and drums by the adjusting screws 35. The efficiency of rolling and calibration is checked judging upon the volume-weight of the concrete.

The thermal treatment which follows the calibration and rolling operation, has nothing in common with the heat treatment used in accordance with the conventional methods, since the thermal treatment according to the invention does not include such stages as the gradual rise of temperature of the slab heating, curing of the workpiece until high-temperature treatment begins to give results, and the steaming of the workpiece.

When the calibrated slab 11 moves through the chamher 2, intensive and high-speed heating of the concrete takes place under the conditions of a high difference of temperatures with such heating being accomplished with the use of steam having a temperature of 105 to 110 C. Thereafter, a temperature of 95 to 98 C. is maintained in the concrete workpiece until the end of the heat treatment, and the duration of the heat treatment in the case of shell-type slabs amounts to lQO min.

Intensive heating of the concrete slab in the front section of the chamber 2 is combined with the application of high pressure to the slab surface by means of the rolls 412 bearing upon the strip 40 for preventing water evaporation, swelling and cracking of the concrete.

The overall length of the heat-treatment period depends upon the properties of the cement and the specidied thickness of the slabs 11, and can be determined experimentally, such as by using three series of specimens to be subjected to heat-treatment during three different periods, for example, 105, 120 and 135 min. The process of the accelerated hardening of the concrete is influa enced mainly by the following factors: stiffness of the concrete mix and the degree of its compacting, since a stiff concrete mix has fine pores which intensively retain water so that the concrete can be heated .to a high temperature without any risk of dehydration and a drop of the moisture content necessary for hydration of cement and hardening of the concrete; heating to a temperature of approximately 100 C. increases molecular pressure in the concrete and intensifies the process of cement hydration thus facilitating extra-quick setting and hardening of the concrete; hermetic sealing and isolation of the concrete during its intensive heating such as by means of a flat cover strip 40 which ensures the required inner micropressure and complete hydration of the cement grains, prevents the movement of water in the concrete mix from places having a lower temperature to places having a higher temperature ensures uniform heating across the entire section of the workpiece, prevents water evaporation from the concrete, and contamination of the concrete with a condensate causing deterioration of the surface layer.

The minimum strength of concrete sufiicient for slab separation and transportation is approximately kg./ cm.

The production of ribles's fiat slabs (or panels) differs from the process described above in that the cavity-forming elements 10 are not placed on the conveyor 3 but reinforcing steel frames corresponding to the ribless design of the slabs are used.

Specifications of present apparatus Maximum speed of plate belt conveyor movement, m./hr. 60 Service (medium) speed of plate belt conveyor movement, m./hr. 30 Apparatus capacity, in terms of slabs rolled,

m? up to Plate belt conveyor width, mm 3600 Standard size of the cavity-forming elements:

300 x 300 x 70 mm. 300 x 600 x 100mm. 300 x 1200 x 220 mm.

Slab maximum dimensions:

Width, mm. up to 3400 Length, mm. up to 12,000 Thickness, mm. up to 340 Temperature of the heat-transfer medium,-

C. u -110 Heat-treatment temperature inside the chamber, C. 96-100 Temperature of the slab accelerated heating,

C. 95-98 Overall duration of the heat-treatment, min. up to Steam consumption, at plate belt conveyor speed of 30 m./hr., kg. 1500 Power of apparatus main drive, kw 15 Total power of apparatus electric motors,

Apparatus overall dimensions:

length (to output end support), in. 94 Width (less drive), m. 5.0 Width (with main drive), In. 7.2 Height above floor level, In. 3.5 A Weight f apparatus metal parts, t 300 The overall size of the structural elements which can be manufactured on the apparatus according to this invention is restricted only by the width of the plate belt con- 'veyor, length of the tipper, and the maximum gap between the convey-or belt and the lower flight of the rolling and calibration arrangement. The minimum possible thickness of the workpiece depends upon the maximum size of the coarse aggregate used, grade of the concrete, and the W99 'Qf reinforcement. The rolled concrete workpieces can have any shape desired, provided one of the workpiece sides is flat.

The types of reinforced-concrete structural elements,

mainly slabs, plates and panels, produced in accordance the area of the slab being up to 30 m and its thickness (or rib height) amounting to 8-20 cm. (FIGS. 9-14).

These shell-type slabs are used for the manufacture of double-layer and triple-layer Wall and ceiling panels with heat and sound insulation for serving as outside and inner walling elements, and also for the assembly of threedimensional units (for example, weather-proof bus stations, transformer substations, two-way underground collectors, etc.). Moreover, the shell-type slabs are used for rural construction, the erection of storehouses and other non-heated buildings, site fencing, irrigation structures, and highway covering elements.

Among the structural elements manufactured with the invention and serving for housing and civil prefabricated large panel construction are the following: outside wall three-layer panels, with their size being equal to that of a two to four room wall, and their thickness being up to 30 cm.; inner carrying double-layer wall panels with sound-insulating liners having an area up to 30 m. and a thickness up to 18 cm.; flat panels of inner carrying walls, with a length up to 6 m., height equal to one story, and thickness up to 25 cm.; flat ceiling slabs, with a size equal to a room ceiling area and a thickness up to 14 cm.; and keramsite-concrete outside wall panels, with a size equal to two or three room wall length, and a thickness up to 32 cm.

The structural elements listed above are suitable for construction of prefabricated houses, such as two-flat and mul-ti-flat two-story houses in rural areas, frameless panel houses of 5 to 16 stories, and framework-type panel houses of 16 to 25 stories in urban areas.

Light-weight shell-type slabs are being ever more widely used as outside fencing elements and roofing elements for industrial buildings. A light weight slab proper, in combination with light, heat and sound insulating materials used as an inter-slab lining makes reinforced concrete elements competitive with multi-layer veneer and wood-fiber panels.

For road construction, ribbed and flat reinforced concrete slabs having a maximum area of m can be manufactured in accordance with the invention.

When the apparatus is equipped with the appropriate devices for prest-ressing steel reinforcement, the list of elements which can be produced is still longer, and includes miscellaneous structural elements for road and transportation construction. In this case, the length of the prefabricated elements used for road and airfield coverings can be increased to reach as much as 6 m. and over, with a simultaneous improvement of their technical and economic properties. Further, it is practicable to employ the invention for the manufacture of railway sleepers, sleeper plates, etc.

I claim:

1. A method for producing concrete and reinforced concrete slabs and substantially flat structural elements, comprising the steps of forming rows of molds on an endless belt defined by lateral walls and transverse partitions, coating the molds with a compound for preventing the concrete from adhering to the mold surfaces, moving the belt at a speed preset in accordance with the time for hardening of the concrete and the length of the belt reserved for the hardening, positioning reinforcing frames and anchor elements into the molds, continuously introducing a concrete mix having a surplus into the molds continuously distributing the mix throughout the full width of the molds, subjecting the molds to vibratory action from above for molding and compacting the concrete mix, cutting oif the surplus concrete mix from the molded slabs to the required thickness, smoothing the concrete surface after the surplus concrete has been cut off, press-gauging the slabs to their final thickness, heat curing the molded and gauged slabs in a curing chamber under hermetic conditions by heating the slabs to approximately C. with steam through a solid heat transmitting medium for accelerated hardening of the concrete with simultaneous additional pressing of the concrete surface to a pressure of not less than 150 g./sq. cm. for preventing swelling thereof, retaining the slabs in the curing chamber for developing the required strength, releasing the slabs from the molds, and discharging the finished slabs.

2. The method as claimed in claim 1 comprising timing the steps in accordance with the rate of movement of the belt and coordinating the rate of movement with the duration of the accelerated hardening of the slabs in the curing chamber.

3. The method as claimed in claim 1 comprising intensively heating the slabs to 95-98 C. within 30-40 minutes and the entire heating to achieve 50-60% of an ultimate strength of the sla'bs being between -120 minutes.

- 4. The method as claimed in claim 1 and for producing slabs having longitudinal, transverse and criss-cross ribbings, comprising positioning cavity defining cores of truncated pyramidical form provided with rounded edges and coated with a compound for preventing the adhering of concrete thereto in the molds with the height, width and length of such cores being dependent upon the thickness of the slab web and the size of the ribbing formed between the cores.

5. The method as claimed in claim 4 further including positioning insert means in the molds for forming openings in slabs.

References Cited by the Examiner UNITED STATES PATENTS 323,818 8/ 1885 Logan 2599 355,876 1/ 1-887 Lesneur 2599 1,513,801 11/1924 Camp 26471 1,694,563 1 2/1928 Ross 2647l 2,025,703 12/ 1935 Baily. 2,569,231 9/1951 Danholf 264-228 2,804,672 9/ 1957 Altschuler 264-229 2,835,016 5/1958 Dixon 264333 FOREIGN PATENTS 11,099 1/ 1928 Australia. 137,045 1/ 1962 Russia. 144,103 l/1962 Russia.

ROBERT F. WHITE, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

R. B. MOFFI'IT, Assistant Examiner. 

1. A METHOD FOR PRODUCING CONCRETE AND REINFORCED CONCRETE SLABS AND SUBSTANTIALLY FLAT STRUCTURAL ELEMENTS, COMPRISING THE STEPS OF FORMING ROWS OF MOLDS ON AN ENDLESS BELT DEFINED BY LATERAL WALLS AND TRANSVERSE PARTITIONS, COATING THE MOLDS WITH A COMPOUND FOR PREVENTING THE CONCRETE FROM ADHERING TO THE MOLD SURFACES, MOVING THE BELT AT A SPEED PRESET IN ACCORDANCE WITH THE TIME FOR HARDENING OF THE CONCRETE AND THE LENGTH OF THE BELT RESERVED FOR THE HARDENING, POSITIONING REINFORCING FRAMES AND ANCHOR ELEMENTS INTO THE MOLDS, CONTINUOUSLY INTRODUCING A CONCRETE MIX HAVING A SURPLUS INTO THE MOLDS CONTINUOUSLY DISTRIBUTING THE MIX THROUGHOUT THE FULL WIDTH OF THE MOLDS, SUBJECTING THE MOLDS TO VIBRATORY ACTION FROM ABOVE THE MOLDING AND COMPACTING THE CONCRETE MIX, CUTTING OFF THE SURPLUS CONCRETE MIX FROM THE MOLDED SLABS TO THE REQUIRED THICKNESS, SMOOTHING THE CONCRETE SURFACE AFTER THE SURPLUS CONCRETE HAS BEEN CUT OFF, PRESS-GAUGING THE SLABS IN THEIR FINAL THICKNESS, HEAT CURING THE MOLDED AND GUGED SLABS IN A CURING CHAMBER UNDER HERMETIC CONDITIONS BY HEATING THE SLABS TO APPROXIMATELY 100*C. WITH STREAM THROUGH A SOLID HEAT TRANSMITTING MEDIUM FOR ACCELERATED HARDENING OF THE CONCRETE WITH SIMULTANEOUS ADDITIONAL PRESSING OF THE CONCRETE SURFACE TO A PRESSURE OF NOT LESS THAN 150 G./SQ. CM. FOR PREVENTING SWELLING THEREOF, RETAINING THE SLABS IN THE CURING CHAMBER FOR DEVELOPING THE REQUIRED STRENGTH, RELEASING THE SLABS FROM THE MOLDS, AND DISCHARGING THE FINISHED SLABS. 